1. Field of the Invention
This invention relates to a process for bleaching pulp with ozone. More particularly, it relates to bleaching pulp at low consistencies with ozone in the presence of a cationic surfactant.
2. The Prior Art
It is known that ozone is an effective bleaching chemical when applied to pulps at consistencies of say from 25 to 65%. High consistency slurries have been used because the bleaching rate of ozone at low consistencies is extremely slow. Brabender et al. in U.S. Pat. No. 2,466,633 were among the first to teach high consistency bleaching pulp with ozone. However, it was felt that early attempts to bleach with ozone were detrimental to the cellulose fibers. Because of the strong oxidizing power of ozone, there is an indiscriminate ozone oxidation attacking carbohydrate and lignin concurrently producing significant degradation of fibers over extended reaction times.
Wade in U.S. Pat. No. 3,318,657 claimed to have overcome this problem by treating cellulose fibers prior to contact with ozone with an alkali metal borohydride. Later, Ancelle et al. in U.S. Pat. No. 3,451,888 disclosed the use of wetted ozonized air as a bleaching agent.
It is evident that the development of a commercially acceptable ozone-based bleaching system would eliminate chlorine containing bleach effluents and reduce chemical costs. It is, therefore, the general object of this invention to provide a commercially acceptable ozone pulp-bleaching process.
Another object of this invention is to provide a process for bleaching pulp with ozone at low consistencies.
Other objects, features and advantages of the invention will be evident from the following detailed description.